What is acceptable air conditioner outlet temperature?

I have a 1996 Nissan Maxima. It was about 95 degrees today (measured with my own thermometer not what the weather report says), and my air conditioner outlet temperature was reading about 50 degrees. that would be temperature differential of about 45 degrees. I had the fan on second lowest out of 4 settings and on recirculation.

Does that seem reasonable?

I had the car for about 4 years now, and the air conditinoner had been all right when I first bought it, but it has been progressively getting warmer. Today, when the outside temperature was registering 95, the car interior would not get cooler than 80. Even when I drove for 20 minutes on the freeway.

Is there an easy way to check whether the air conditioner is working properly?

Approx. 40 degrees F is what you’re shooting for.

Have a qualified mechanic check it out.

Older cars will loose refrigerant over time and require a “recharge” at some point.

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I’ve read manuals that stated a 45 degree temperature drop is normal and acceptable; however, I don’t buy that at all.
My feeling is that the outlet temps should be down in the high 30s/very low 40s at a minimum on a 90 degree day.
Some years back on my now gone Mercury I had the A/C on that one putting out 25-30 degree air on a 100+ degree day although I consider this one more of an anomaly.

The best thing that can be done is to connect a full gauge set and see what’s going on with the pressures on both the high and low sides. If the pressures are fine then one should consider the possibility of a blend door not functioning correctly.

You might also raise the hood and look at the evaporator outlet fittings, the accumulator, etc. for condensation. If there’s any humidity to speak of you should see these parts sweating and there should be a constant condensation drip under the car if the A/C is functioning even halfway like it should.

Me being from GM have been trained to figure in the humidity but the practice draws much “flack” here. Use a few degrees above what low side temp is… Take a look at gague head you will see that temp/pressure is roughly porportinal for both R12 R134A.

I agree that low side system pressure is a good indicator of the outlet air temps. If someone has 50ish PSI on the low side then they have a problem in my opinion.

The car is 15 years old and odds are that it’s a bit down on the refrigerant charge due to leakage.

My 1999 Camry got down to about 42F on a 95F day system on recirc and full fan.

My '97 Escort hits 40 pretty much regardless of the temps (max I get is about 100).

I recently had a general purpose shop (my mistake) evacuate & recharge my Silhouette AC - they assured me that with such a large system (front & rear w/ about 3lb refrigerant) the 50 degrees from the vent on a 90 degree day was about as good as it would get. Bunk. I’m going to get it to the local specialists. I think you should too.

Personally I don’t think a 45 degree drop is unreasonable. The temp out the vent will be dependent upon the ambient temp. The system only removes heat, and its capacity to do so is finite, meaning that as the ambient temp rises so too does the vent outlet temp.

One thing it also does that makes it seem more efficient is that it removes moisture also. The dried cabin air doesn’t seem as hot, becuause it has better capacity to absorb moisture from your skin which is how your body dissipates heat.

NOone in the AC biz uses how much drop you get as a parameter in judging AC performance. Not how GM, or BMW taught me, where did this method come from?

It is not part of the ASE cert. test I took and passed, or the refridgerant handling class or the Community College class, or the GM FSM.

And your perception of how good a job is done has the humidity of the air around you as one of its parameters.

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Checking the vent outlet temp is part of the job according to the factory service manuals on the cars that I’ve been involved with although I don’t consider it to be the first priority.
First thing is to connect the gauges and see what the high/low pressures are. Checking outlet temps should be saved for a test run down the road after everything is buttoned up.

Some of us (myself included) seem to have missed an important point:
“I had the car for about 4 years now, and the air conditioner had been all right when I first bought it, but it has been progressively getting warmer.”

Since the performance of the system seems to have deteriorated, an automotive AC shop visit is in order. Only hands-on can the performance of the system be evaluated.

Have it serviced. It sounds like your are on less expensive end of the essentially two sided spectrum of AC repair.

IMHO AC repair is either $60 or $1500 never typically between.

If the evaporator temperature drops below 32* icing will occur. And coincidentally, a low pressure of 35 psi indicates an evaporator temperature of 35*. All things being perfect the outlet temperature could be down to 40* but 45* is great and 50* is acceptable when the ambient temperature is in the upper nineties and the humidity above 80%. Realil$tically speaking, if the system is reliably operating and relatively quickly dropping the cabin temperature to a comfortable level ENJOY it. Don’t SWEAT the small stuff.

AC performance is anything but “small stuff” here in Tucson. Temp and pressure are not directly porportinal (take a look at the gague head).

Where is that guy that argued endlessly that humidity does not need to be taken into condideration due to the use of the vehicles recirculation and inherint moisture removal for the air properties of an autos AC system? no one chimed in to say he was wrong then.

I’m in KY where we’ve had temps in the 90s with high relative humidity. Thus i’ve still observed duct temps in the low 40s. I think you mean well but the o/p should get thee to an a/c tech. In my experience an a/c job is money well spent.

I have never suggested a DIYer add AC work to his list,I was approaching this thread to see where this “if it drops the temp by 45F then all is well” rule came from.

Jeff are you suggesting that humidity should not be taken into account when doing an AC performance test? by the way I am a very well certified/experienced AC tech.

I agree. Mine blows 34 degree air at 95 degrees. But mine isn’t 14 years old either. After all this time, I’m sure the Maxima needs a recharge. Refrigerant does slowly seep out of the system over time. While you’re in there, have 'em pressure check the system to be sure you don’t have an actual leak. Much cheaper to fix that now than to keep adding refrigerant.

Car ac systems are pretty basic. If it is not cooling as well as it used to make sure the condenser is clean. If it is check the compressor belt and make sure it is in good condition and not slipping. Then go to the parts store and buy a can of refergant with the cheap gauge. Check the pressure based on temperature. Put a good thermometer in the center vent and slowly add freon. Add a little and let it sit for a minute or two. Work between the pressure and the air temp at the vent.

Matt , you have tagged on to a 9 year old thread and telling people to just add refrigerant is irresponsible.

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